Squid and Octopus Populations on the Rise

Human alteration of the environment has plagued the world’s oceans, contributing to both rising temperatures and acidification of waters. This change has led to the depletion of many marine species, but, as a recent study in Current Biology reveals, cephalopod populations, including squid, octopuses, and cuttlefish, have increased globally since the 1950s.

In the 1990s, scientists noticed a growth in cephalopod catches at fisheries across the world. From this data, scientists speculated that the cephalopod population was increasing. Because misreporting catch numbers is common and numerous factors can influence them, however, they could not conclude that the cephalopod population was increasing without a more rigorous study.

Dr. Zoe Doubleday, a marine biologist at the University of Adelaide in Australia and lead author of the study, and her research team sought out data that would provide a more reliable estimate of population numbers. After months of research, they obtained 60 years of scientific survey data and fisheries records with which to work.

A thorough evaluation of this data provided a clear conclusion: worldwide cephalopod populations have increased significantly since the 1950s. Cephalopods, an invertebrate group, include squid, octopuses, and cuttlefish. Why are cephalopod populations, unlike most marine species, booming? The study’s researchers say that the group is very efficient at adapting to changes in the environment, enabling them to overcome the disturbances that have contributed to the depletion of other species. Although they only live for one to two years, they produce many eggs, and these eggs have low mortality rates, allowing them to adapt rapidly to environmental changes.

The researchers do note, however, that they can only speculate about which environmental changes are responsible for the increasing population. It is possible that when humans catch predators of cephalopods, they create a gap in the food chain for this adaptable species to fill. Another factor that may facilitate the population growth is rising temperatures. Warmer temperatures may make them reproduce more quickly and, in turn, increase the rate at which the population increases. Dr. Doubleday told Science Magazine that pinpointing causal relationships will require more research, noting that “it’s all speculation, what’s causing them to increase.”

Regardless of the cause, the population increase could dramatically affect our oceans. While it could benefit the sharks, whales, and large fish that feed upon them, it could also lead to unstable fishing profits. The researchers acknowledge that we will only realize this impact with time.